Analysis of mutations in multiple loci of Neisseria gonorrhoeae isolates reveals effects of PIB, PBP2 and MtrR on reduced susceptibility to ceftriaxone

Abstract

Objectives: To elucidate loci in Neisseria gonorrhoeae implicated in reduced susceptibility to ceftriaxone.

Methods: N. gonorrhoeae isolates were collected in Shanghai, China, in 2005 and 2008. Twenty-eight isolates with reduced susceptibility to ceftriaxone (CRO(Red); MIC = 0.125-0.25 mg/L) were studied for mutations in PorB (porB), MtrR (mtrR), PBP2 (penA) and PBP1 (ponA). The mutation profiles of the 28 CRO(Red) isolates were compared with those of 32 ceftriaxone-susceptible isolates (CRO(S); MIC = 0.004-0.016 mg/L). porB-based DNA sequence typing and N. gonorrhoeae multi-antigen sequence typing (NG-MAST) analyses were performed.

Results: Significantly more CRO(Red) isolates (89.3%) exhibited a PIB phenotype as compared with the CRO(S) isolates (59.4%) (P = 0.02). Double mutations (G45D/H105Y or A39T/H105Y) in MtrR were associated with CRO(Red) phenotypes. A 'wild-type' MtrR protein characterized CRO(Red) isolates (50.0%, 14/28), while a single H105Y mutation was observed only in CRO(S) isolates (43.8%, 14/32). Both CRO(Red) and CRO(S) isolates carried an '-A' deletion in the mtrR promoter. Six of 15 mutation patterns observed in PBP2 were new. Mutation patterns XIII (17.9% of CRO(Red) isolates) and XVII or XVIII (25.0% of CRO(Red) isolates) of PBP2 comprised A501V/G542S or A501V/P551S double mutations and were associated with a CRO(Red) phenotype. The mosaic PBP2 (pattern X) was not observed. The L421P mutation in PBP1 was observed in all CRO(Red) and in 97.0% of CRO(S) isolates. CRO(Red) isolates were non-clonal.

Conclusions: Reduced susceptibility to ceftriaxone in N. gonorrhoeae is mediated by porB1b alleles and is associated with specific mutations in PBP2 and in the DNA binding and dimerization domains of MtrR.